1. Field of the Invention
The present invention relates to a vacuum pressure-adjusting apparatus capable of supplying an adjusted predetermined vacuum pressure to a fluid pressure-operated apparatus which is operated by the vacuum pressure.
2. Description of the Related Art
A process has been hitherto carried out, in which a workpiece is sucked and transported, for example, by using a suction means such as a suction pad in accordance with an action of the vacuum pressure. When the vacuum pressure is supplied from a vacuum pump to the suction pad, a vacuum pressure-adjusting apparatus such as a vacuum regulator is provided between the vacuum pump and the suction pad, for adjusting the vacuum pressure from the vacuum pump to have a predetermined value so that the vacuum pressure is supplied to the suction pad.
Such a vacuum regulator concerning the conventional technique is shown in FIG. 4 (see Japanese Laid-Open Patent Publication No. 7-295655).
The vacuum regulator 1 comprises a housing 6 formed with a vacuum port 3 which is connected to a vacuum pressure supply source 2 such as a vacuum pump, and a pressure regulator port 5 which is connected to a vacuum pressure-operated apparatus 4 such as a suction pad.
A hole 7, which extends in the axial direction, is formed at a central portion in the housing 6. A valve stem 8 is provided slidably in the hole 7. A valve plug 11, which is urged by a spring force of a first compressive coil spring 9 to seat on a valve seat 10, is coupled to the valve stem 8. A seal member 12, which is composed of an elastic member such as rubber to make abutment against the valve seat 10, is secured to the valve plug 11. In this arrangement, the valve plug 11 is urged by the spring force of the first compressive coil spring 9 so that the valve-closed state is always given. The seal member 12, which is composed of the elastic member, is seated on the valve seat in a state of biting into the valve seat 10 which is composed of an annular projection (see FIG. 5).
An atmospheric chamber 14 which communicates with the outside via a communication hole 13, and a vacuum chamber 16 which communicates with the pressure regulator port 5 via a bypass hole 15 are formed and comparted by a diaphragm 17 in the housing 6.
A communication port 19, which is opened and closed by the valve stem 8, is formed in an interlocking disk 18 which is displaceable integrally with the diaphragm 17. A second compressive coil spring 20, which has a spring force to urge the valve plug 11 in a direction to make separation from the valve seat 10, is arranged at the inside of the housing 6. The second compressive coil spring 20 is designed such that the spring force thereof is adjusted by a handle 21.
In this arrangement, the vacuum pressure of the pressure regulator port 5 is set by the second compressive coil spring 20. When the vacuum pressure is not more than a predetermined pressure, the atmospheric air is supplied via the communication port 19 to the pressure regulator port 5.
However, the vacuum regulator 1 concerning the conventional technique described above involves the following inconvenience. That is, when the valve plug 11 is in the valve-closed state, the seal member 12 of the valve plug 11 is in the state of biting into the valve seat 10 by the aid of the spring force of the first compressive coil spring 9. Therefore, even when the handle 21 is operated and rotated to finely adjust the predetermined vacuum pressure, the response sensitivity is blunt, because of the following reason.
That is, when a predetermined vacuum pressure is reset to another finely adjusted vacuum pressure, it is necessary that the valve plug 11 is reliably separated from the valve seat 10 to give the valve-open state, and the vacuum port 3 is communicated with the pressure regulator port 5 to change the vacuum pressure supplied from the pressure regulator port 5. In order to give the valve-open state of the valve plug 11, it is necessary that the valve plug 11 is firstly displaced slightly in an amount of the biting of the seal member 12 into the valve seat 10, and then the seal member 12 of the valve plug 11 is separated from the valve seat 10 to form a predetermined clearance. However, in the case of the vacuum regulator 1 concerning the conventional technique, a so-called dead zone appears, in which the vacuum pressure is not changed even when the valve plug 11 is slightly displaced in the amount of the biting of the seal member 12 into the valve seat 10. For this reason, it takes a long time until the vacuum pressure begins to change, and the response speed is slow.
Further, the vacuum regulator 1 concerning the conventional technique involves the following inconvenience. That is, when a predetermined vacuum pressure is finely adjusted, and it is reset to another vacuum pressure, then the setting accuracy of the reset vacuum pressure is inferior, and the setting operation is time-consuming and complicated, because the dead zone appears as described above.